One of the most misunderstood aspects of US tariffs is stacking — the way tariffs from different legal authorities add up on the same import. After the SCOTUS ruling struck down IEEPA tariffs and replaced them with a 10% Section 122 tariff — which expired at its 150-day statutory limit on July 24, 2026 and was replaced by the Section 301 forced-labor tariff (10% for most economies, 12.5% for a 46-economy list including China) — and with steel/aluminum doubled to 50%, the stacking math has changed significantly. Understanding tariff stacking is essential for accurate cost calculations.
What Is Tariff Stacking?
Tariff stacking occurs when multiple tariff programs apply simultaneously to the same import. Each tariff comes from a different legal authority and is assessed independently. The US currently has three main tariff regimes that can stack: the base reciprocal tariff (the Section 301 forced-labor tariff that replaced Section 122 on July 24, 2026 — 10% for most economies, 12.5% for a 46-economy list that includes China, Vietnam, and Thailand), Section 232 tariffs (50% steel/aluminum, 50% copper, 25% autos, 25% semiconductors), and Section 301 tariffs (7.5-100% on Chinese goods). When a product falls under multiple programs, you pay all of them — they don't replace each other, they add up.
Real-World Stacking Examples (Post-SCOTUS)
Chinese steel articles: 50% Section 232 + 25% Section 301 = 75% total duty — the base reciprocal tariff does NOT stack on the Section 232 metal content. Chinese electric vehicles: 2.5% MFN + 12.5% base reciprocal + 100% Section 301 = 115%. Chinese solar panels: 12.5% base reciprocal + 50% Section 301 = 62.5%. Vietnamese steel articles: 50% Section 232 (the base reciprocal tariff is excluded on the metal). German automobiles: 25% Section 232 auto (the base reciprocal tariff is excluded on Section 232 goods). Japanese steel articles: 50% Section 232. UK steel: 25% Section 232 (EPD rate). The key pattern: goods already subject to Section 232 (steel, aluminum, copper, autos) are carved out of the base reciprocal surcharge to the extent the 232 duty applies — the base reciprocal tariff reaches only any non-metal content. Section 301 and the MFN base rate, by contrast, do stack.
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Anti-Stacking Rule: Section 232 Goods Are Excluded from the Base Reciprocal Tariff
The most important anti-stacking rule is general, not country-specific: goods already subject to a Section 232 tariff (steel, aluminum, copper, automobiles) are NOT also charged the 10% base reciprocal surcharge to the extent the Section 232 duty applies. So a car subject to the 25% Section 232 auto tariff pays 25%, not 25% + 10%, and an article wholly of steel pays its 50% Section 232 rate, not 60%. The base reciprocal tariff reaches only any non-metal content of a Section 232 article. (On top of this, USMCA-qualifying vehicles, steel, and aluminum from Canada and Mexico can avoid the Section 232 tariff entirely.)
USMCA Exemption: Canada/Mexico Steel/Aluminum
Separately, USMCA-qualifying steel and aluminum from Canada and Mexico can be exempt from the Section 232 steel/aluminum tariff (50%) altogether. Non-USMCA Canadian steel pays 50% Section 232 — and because Section 232 goods are excluded from the base reciprocal surcharge on their metal content, the rate is 50%, not 60%. The UK pays a reduced 25% Section 232 rate on metal articles under the Economic Prosperity Deal.
Why Effective Rates Differ from Announced Rates
When tariff rates are discussed in the media or in trade negotiations, the number cited is usually just one component. 'A 10% base reciprocal tariff' doesn't include Section 232 (50% on steel) or Section 301 (25-100% on Chinese goods). Always calculate the full stacked rate for your specific product and country combination. The difference between the headline rate and the effective rate can be 25-75 percentage points or more.
Key Takeaway
Tariff stacking means your actual duty rate is often 2-8x the headline number. China steel at 75%, Chinese EVs at 115%, and Chinese solar at 62.5% are common examples. Always check all three tariff programs (the base reciprocal tariff, Section 232, Section 301) for your product. USMCA and UK EPD offer limited relief on certain products.
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